Opioid drugs are widely prescribed to patients suffering from chronic pain despite the fact that we still know very little about the impact of opioids, chronic pain, and both conditions on brain function. The main goals of this project are to (i) provide novel evidence for the functional interaction between reward-, pain-, and memory-processing circuits, (ii) determine how this interaction is affected by chronic pain, and (iii) show whether restoring the function of these circuits can reduce pain and opioid addiction. Based on our recent and pilot studies, we posit that functional changes in projections from the mesolimbic ventral tegmental area (VTA) to DH, carrying information on pain and reward, alter hippocampal plasticity and enable the DH-RSC memory circuit to gain excessive control over both chronic pain and opioid craving. Dissecting the role of individual neurotransmitter circuits is essential for the better understanding of sex-specific differences in opioid seeking, showing higher susceptibility of females to aversive triggers and higher susceptibility of males to rewarding triggers. Specific Aim 1 is designed to determine the role of VTA-DH projections in chronic pain and opioid craving using chemogenetic inactivation of glutamatergic, GABAergic, dopaminergic pathways. Specific Aim 2 will use similar approaches to determine the role of glutamatergic DH-RSC and RSC-VTA projections. Specific Aim 3 will show whether sex-specific activity of discrete VTA-DH-RSC projections is sufficient to induce pain and opioid craving. Specific Aim 4 will integrate key findings of Project 3 with findings of the other projects of the Center by examining the relationship between memory and reward circuits (Project 2), the relationship between transcriptional changes in the VTA and the reorganization of VTA-DH circuits (Project 4), the impact of individual VTA-DH-RSC pathways on whole brain activity and connectivity (Project 1), and the relevance of our findings for patient populations (Project 1). We expect to show that originally distinct pathways processing pain, reward, and memory, alter their stimulus specificity during chronic pain and addiction, causing changes of DH plasticity and reorganization of the VTA-DH-RSC circuit. The circuit, transcriptional, and synaptic mechanisms identified in this project will serve as a basis for development of new treatments for chronic pain and addiction. !